This invention concerns improvements in the use of small diameter low profile dilatation catheters used to dilate an obstructed artery such as in angioplasty and, particularly, coronary angioplasty. In performing coronary angioplasty, it often occurs that the physican may wish to use a catheter different than the one originally inserted into the patient. For example, this may occur if the initial selection of catheter balloon size was inappropriate to treat the obstruction (stenosis) or if some other event occurs that would make the use of a different catheter desirable. When the catheter is of the type that uses a separate movable guidewire, for example, as disclosed in U.S. Pat. No. 4,545,390 (Leary), the catheter may be exchanged in a well-known procedure in which an exchange wire is substituted for the movable guidewire (or the length of the guidewire is extended with an extension wire); then the catheter is withdrawn over the exchange wire and the replacement catheter is threaded over the exchange wire and is thereby guided to the stenosis. By maintaining the guidewire in position in the stenosis during the exchange procedure, the replacement catheter is easily and quickly advanced to the stenosis.
The foregoing catheter exchange procedure is not usable with small diameter low profile dilatation catheters of the type that incorporate an integral guidewire because the balloon catheter cannot be separated from the guidewire. Thus, when it is desired to exchange such a fixed wire dilatation catheter for another catheter, such as a catheter utilizing a movable guidewire, the procedure has required withdrawal of the entire fixed wire catheter. Withdrawal of the fixed wire catheter, however, results in loss of position of the catheter in the stenosis. Consequently, there is nothing in the patient's blood vessel to guide the succeeding catheter to the stenosis. As a result, a new guidewire must be inserted and remanipulated through the patient's arterial system to reach and then cross through the stenosis, thereby to provide a guiding path over which the succeeding balloon catheter can be advanced. The replacement of a integral fixed wire catheter with a guidewire necessarily involves time consuming manipulation and steering of the guidewire to advance it to and through the stenosis. The additional procedure increases the risk to the patient.
It would be desirable, therefore, to provide a means by which catheter exchanges involving a small diameter low profile dilatation catheter having an integral guidewire could be effected easily, quickly, without loss of position and with minimal trauma. It is among the objects of the invention, to provide such a system and, particularly, to provide a guidewire that can be guided to the stenosis by the fixed wire dilatation catheter.